Abstract: Commonly?used acid viscosifiers during acid fracturing are mostly high?molecular polymers of polyacrylamide. These viscosifiers still have some viscosity after degradation and remain in formations after acid fracturing, which may cause damages to reservoirs and influence the acid fracturing effect directly. 3 types of residual acids of polymer acid viscosifier (gelled acid, crosslinked acid and temperature?controlled sticking acid ) are prepared, and experiments on the damages of these 3 residual acids to high?permeable and low?permeable carbonate cores are carried out. The results show that all the 3 residual acids have greater damages to matrix permeability of high?permeable carbonate cores than that of low?permeable cores, i.e., the larger the initial core permeability and, the more developed the core pores are, the more serious the damage from products degraded by large?molecule polymers will be. However, the filter cakes produced by the 3 residual acids have relatively low damages to core permeability, which might not be the key factor for the reservoir damage